The objective of this proposed project is to elucidate the mechanisms that control lens cell differentiation during lens morphogenesis and lens growth. It is generally accepted that the optic plate induces lens morphogensis. However, earlier inductive interactions may be involved in lens determination as indicated from experiments with amphibians. Therefore, the aim of one section of the work is to determine at what stage in development the rat lens differentiates from the ectoderm. This problem will be examined by tissue explantation and recombination experiments. The presence of crystallins as shown by immunofluorescence will be the test for lens differentiation. Lens development involves the co-ordinated expression of crystallin genes. Experiments are planned to determine whether the optic cup environment induces synthesis of Beta- and gamma-crystallins and if so, which component(s) of this environment provides the inducing signal(s). This will involve lens inversion experiments 'in vivo' as well as lens tissue explanation and recombination with different components of the optic cup environment. The appearance of Beta- and gamma-crystallins will be detected by immunofluorescence. Other explantation and recombination experiments with interposed membranes are designed to determine whether the optic plate/cup produces a sequence of signals specific for the induction of alpha-crystallin synthesis on the one hand and Beta- and gamma-crystallin synthesis on the other. The changing morphology of tissue interactions in these experiments as well as 'in vivo' will be examined by electron microscopy, and these observations together with the experimental results should help elucidate the mechanism of lens induction. This research work will provide general information on the control of lens cell differentiation in mammals including humans, which is essential for the understanding of normal and abnormal lens growth.